Magnetic levitation (or “maglev” as it is known) is a method of transport that moves vehicles in magnetic suspension along a guideway. Maglev can be faster, quieter, and more efficient than conventional railroad. Moreover, maglev eliminates the wear and vibration from the steel-on-steel contact of conventional railroads, greatly reducing right-of-way maintenance.
There are currently two principal approaches to maglev, electromagnetic suspension (EMS) and electrodynamic suspension (EDS). In EMS, as exemplified by the German Transrapid Maglev, electromagnets on the train attract iron components in the guideway for levitation. The resulting equilibrium is, however, highly unstable so high-speed electronics on the train is used to adjust the current in the electromagnets hundreds of thousands of times per second to achieve stable levitation. In EDS, as exemplified by the Japanese SCMaglev, superconducting magnets on the train induce currents in induction coils in the guideway. Repulsion and attraction of the magnets to these currents then create stable levitation.
Both EMS and EDS systems require energy for levitation and stabilization. In EMS, dissipation in the electromagnets on the train consumes energy. In EDS, dissipation of the eddy currents in the guideway's induction coils consumes energy. In addition, there is substantial cost associated with powering electromagnets and/or building systems with superconducting magnets.
A third alternative, described by Post et al. in U.S. patent publication number 2005/0204948, is a maglev system in which the levitation force is created by attraction of permanent magnets on the vehicle to iron yokes in the guideway. The challenge in this approach is Earnshaw's Theorem, which states that no static configuration of permanent magnets and ferromagnetic materials can provide stable levitation. Thus the levitation created by the permanent magnets described in Post et al. is stable vertically but unstable horizontally. To address this instability, Post et al. describes a stabilization system based on EDS-style electromagnetic attraction and repulsion. Briefly, Post et al. disclose a technology known as “Inductrack III” based on one-dimensional Halbach array magnets. In some embodiments, this stabilization system operates according to the null-flux principle, in others it does not.
The maglev system in Post et al. works well, but in order to create a stabilization system with sufficient horizontal stiffness, the Halbach arrays in the stabilization system must have closely-spaced poles. As a consequence, at typical interurban speeds, the stabilization system operates at an AC frequency of many hundreds of Hertz. Induction coils for such frequencies can be made using woven copper Litz wire and other technologies designed for high-frequencies, but the resulting system is more expensive and less efficient than systems operating at lower frequencies.